Selection of Naturally Occurring Stress Tolerant Rhizobium

Abstract

Symbiotic nitrogen fixation is commonly limited by soil infertility conditions, especially phosphate deficiency, acidity and salinity. Phosphate sorption buffers phosphate at low concentrations in soil solutions, the resulting immobility causing deficiency to plants in most soils with moderate or high degrees of mineral weathering. Acidity, the consequence of prolonged leaching with inputs of carbonic, nitric, and sulphuric acid, is attended by calcium deficiency and toxicities of aluminum or manganese, and is common where the rainfall is high, the landsurface old, or the agriculture old and productive. Salinity, the accumulation of leachable products, attended by alkalinity and sodicity, is common in irrigated agriculture of arid regions. Some legumes become specially sensitive to these disorders when they are dependent on symbiotic nitrogen fixation.